Add option to build TWRP with toolbox instead of busybox

Makes a smaller TWRP
Uses mksh for shell

Change-Id: If78d7745dda8919fcb2e9c9b60c6696063c14114
diff --git a/prebuilt/Android.mk b/prebuilt/Android.mk
index b5da5a9..1f784d3 100644
--- a/prebuilt/Android.mk
+++ b/prebuilt/Android.mk
@@ -13,7 +13,11 @@
 RELINK_SOURCE_FILES += $(TARGET_RECOVERY_ROOT_OUT)/sbin/dump_image
 RELINK_SOURCE_FILES += $(TARGET_RECOVERY_ROOT_OUT)/sbin/flash_image
 RELINK_SOURCE_FILES += $(TARGET_RECOVERY_ROOT_OUT)/sbin/erase_image
-RELINK_SOURCE_FILES += $(TARGET_OUT_OPTIONAL_EXECUTABLES)/busybox
+ifneq ($(TW_USE_TOOLBOX), true)
+	RELINK_SOURCE_FILES += $(TARGET_OUT_OPTIONAL_EXECUTABLES)/busybox
+else
+	RELINK_SOURCE_FILES += $(TARGET_OUT_EXECUTABLES)/mksh
+endif
 RELINK_SOURCE_FILES += $(TARGET_RECOVERY_ROOT_OUT)/sbin/pigz
 RELINK_SOURCE_FILES += $(TARGET_RECOVERY_ROOT_OUT)/sbin/dosfsck
 RELINK_SOURCE_FILES += $(TARGET_RECOVERY_ROOT_OUT)/sbin/dosfslabel